1. Field of the Invention
The present invention relates to a gas exchange apparatus employing the silicone rubber hollow fiber composed of a silicone rubber composition for use as an artificial lung by being connected to the external blood circulation circuit, an artificial "gill" as a liquid-to-gas phase gas exchanger, and further an oxygenator and disoxidizer for liquid and gas.
2. Brief Description of the Prior Art
As a conventional gas exchanger, there has been known a membrane-type artificial lung disclosed in Japanese Patent Publication No. 3-60508 (1991), in which gas exchange operation is performed through a porous gas exchange membrane having a plurality of minute or fine openings formed therethrough and serving as gas flow passages, wherein a kind of fine particles are maintained in the fine openings to reduce the sectional area, and, in addition, an anti-coagulant for blood is retained in the fine particles themselves or between these particles. Such a retention function of the agent contributes to prevent leakage of components of blood, such as water or, during a long-term circulation, and also to prevent production of thrombus on the surface of gas exchange membrane, thereby the out-body circulation being enabled with a small amount of heparin supplement.
However, the gas exchange rate was not satisfactory in either of the conventional gas exchanger, since fine particles are confined in fine openings using "porous hollow fiber" for preventing sealum leakage in the first example, and "silicone membrane hollow fiber" having an increased wall thickness is used in the second embodiment. Therefore, there have been problems, when the exchange rate is increased, the dimension of the apparatus, that is, of the artificial lung increases, resulting in an increased quantity of blood, namely the priming volume, which is filled in the apparatus. In contrast, the reduced priming volume, although providing a small size, the quantity of gas exchange is accordingly decreased, and, therefore, the gas exchange rate is lowered.
As a conventional silicone rubber hollow fiber in use for gas exchangers, using a silicone rubber composition, there was a Japanese patent application No.61027/1996 proposed by the same applicant.
The hollow fiber of the invention is formed of a silicone rubber composition of a blend of silicone rubber compound and liquid silicone rubber or silicone oil, and may be produced by setting the ratio of sectional area S.sub.1 :S.sub.2 in the range of 1:0.5 to 1:0.01 when the silicone rubber composition is extruded in a form of tube and oriented under heating in a vulcanizer, wherein S.sub.1 is a sectional area of a tube extruded from a nip between a die and a nipple of an extruder and S.sub.2 is a sectional area of a tube oriented.
The outer diameter of the hollow fiber obtained is less than 300 microns and wall thickness thereof is less than 50 microns. SS are values obtained by the following equations. EQU S.sub.1 =.pi.(r.sub.1 /2).sup.2 -.pi.(r.sub.2 /2).sup.2 EQU S.sub.2 =.pi.(r.sub.3 /2).sup.2 -.pi.(r.sub.4 /2).sup.2
Where, r.sub.1 : an inner diameter of the die;
r.sub.2 : an outer diameter of nipple;
r.sub.3 : an outer diameter of hollow thread; and
r.sub.4 : an inner diameter of hollow thread.
The silicone rubber composition aforementioned is formed by adding a silica as a filler to a silicone rubber compound of dimethylsiloxane and/or dimethylvinylsiloxane as a silicone rubber compound and making use of addition curing-type silicone rubber compound having a hardness of more than 75 (JIS-A) measured by JISK-6301 and a tear strength of more than 40 Kg/cm (Type-A), an organopolysiloxane having a viscosity in the range of 100 tO 100,000 poise at 25.degree. C. containing a vinyl group as an aforesaid silicone rubber and an silicone oil having the same viscosity as that of the organopolysiloxane as above-mentioned silicone oil.
Since the conventional silicone rubber composition is, as described above, formed by mixing a silicone rubber compound with a liquid silicone rubber or silicone oil, a silica agglomerated in the silicone rubber may be dispersed uniformly. Therefore, the conventional silicone rubber becomes a state which cannot be easily cut even the silicone rubber composition is extruded in the form of tube. And also, since the conventional silicone rubber composition is, as described, formed by mixing a silicone rubber compound with a liquid silicone rubber or silicone oil, the chain of high polymer interlocking in the silicone rubber is unravelled, the orientation property of the silicone rubber can be remarkably improved. For the reasons as above, the conventional silicone rubber composition is available to produce a fine and thin-gage silicone rubber hollow fiber having an outer diameter of less than 300 microns and a wall thickness of less than 50 microns.
While the hollow fiber itself could be produced by the conventional silicone rubber composition since the orientation treatment is carried out under a decrease of plasticity by mixing an uncured silicone rubber composition, there is a case where the hollow fiber has the tensile loading (M.sub.100) (100% modulus of which is not sufficient, that is less than 5 grams is produced when the wall thickness is less than 40 microns. Therefore, there occur the troubles such as an elongation set or cut-through of the hollow fiber at a fabrication step, which gives rise to a problem that only a hollow fiber having a wall thickness of approximate 50 microns can be stably produced.